Loader bucket position maintaining system

ABSTRACT

A loader bucket mounted on boom arms, with a hydraulic cylinder on the boom arms for positioning the bucket thereon; valve means for controlling the hydraulic cylinder; a manually operated lever for setting the valve means for correspondingly positioning the bucket; a feedback linkage interconnecting the bucket and valve means for controlling the valve means, and thereby controlling the hydraulic cylinder, by the position of the bucket, according to the setting by the manually operated lever; and cam means on the boom arms for controlling the valve means according to vertical movements of the boom arms and which together with the feedback linkage maintain the bucket in set position through the vertical movements of the boom arms.

[ 1 Mar. 25, 1975 1 1 LOADER BUCKET POSITION MAINTAINING SYSTEM [75] Inventor: Donald W. York, Battle Creek,

Mich.

[73] Assignee: Clark Equipment Company,

Buchanan, Mich.

[22] Filed: July 9, 1970 [21] Appl. N0.: 53,550

[52] U.S. C1. 214/763, 214/140 [51] Int. Cl E02f 3/86 [58] Field of Search 214/140, 762, 763, 771,

[56] References Cited UNITED STATES PATENTS 3,087,636 4/1963 Weaver ..214/1Rc1v1x 3,220,581 11/1965 Pedersen 1. 214/764 3,410,433 11/1968 Brown 1 1 214/763 3,487,968 1/1970 Long 214/764 3,713,557 1/1973 Seaberg 214/763 FOREIGN PATENTS OR APPLICATIONS 847,656 9/1960 United Kingdom 214/] CM Primary Examiner-Robert J. Spar Assistant Erazniner-leslie I, Paperner Attorney, Agent, or Firm-Jack E. Toliver [57] ABSTRACT A loader bucket mounted on boom arms, with a hydraulic cylinder on the boom arms for positioning the bucket thereon; valve means for controlling the hydraulic cylinder; a manually operated lever for setting the valve means for correspondingly positioning the bucket; a feedback linkage interconnecting the bucket and valve means for controlling the valve means, and thereby controlling the hydraulic cylinder, by the position of the bucket, according to the setting by the manually operated lever; and cam means on the boom arms for controlling the valve means according to vertical movements of the boom arms and which together with the feedback linkage maintain the bucket in set position through the vertical movements of the boom arms. 1

13 Claims, 5 Drawing Figures HEN IEO HAR 2 519. 5

E, El

FIG. 4

INVENTOR DONALD W. YOR K ATTORNEY LOADER BUCKET POSITION MAINTAINING SYSTEM OBJECTS OF THE INVENTION A broad object of the invention is to provide a loader bucket construction and system of operating the bucket with novel means for moving the bucket to a predetermined position, such as upright or level position, and for maintaining it in such position in all positions of the boom arms.

Another object is to provide a loader bucket construction of the kind just referred to and including manually manipulable means for predetermining any desired positioning of the bucket.

A still further object is to provide a loader bucket construction of the foregoing character in which the bucket may be pre-positioned in any desired position within a wide range, and further wherein the positioning may be in infinitesimal increments, as contrasted with step-by-step positioning.

A still further object is to provide construction of the character just immediately referred to wherein the manually manipulable means may be moved to any desired position and wherein it remains in such position after being released, and without manual control for holding it in its set position.

A still further object is to provide a construction of the foregoing character in which the means for moving the bucket is of hydraulic nature and which includes valve means for controlling the hydraulic fluid wherein the valve means includes a housing and a'spool, and wherein the valve may be actuated as by moving the housing by the manually manipulable lever and by movement of the bucket, and moving the spool by the movement of the boom arms, wherein the respective movements of the housing and the spool are additive or compensating, whereby to perform an automatic valve limiting operation for predetermining the final position ofthe bucket according to the setting of the manual lever, and in all positions of the boom arms in their vertical movements.

DESCRIPTION OF A PREFERRED EMBODIMENT In the drawings:

FIG. I is a small scale side elevational view of a trac tor loader embodying the features of the present invention, showing the boom arms in lowered position in full lines and in raised position indot-dash lines;

FIG. 2 is a larger scale view of the boom arms and bucket, and the hydraulic system for moving the bucket and maintaining it in the desired position;

FIG. 3 is a fragmentary view of certain control elements of FIG. 2 in alternate positions;

FIG. 4 is also a fragmentary view of certain control elements of FIG. 2 in alternate positions; and

FIG. 5 additionally is 'a fragmentary view of certain control elements of FIG. 2 in alternate positions.

Referring in detail to the drawings, FIG. 1 shows a tractor loader of the character to which the present invention is particularly applicable. The tractor loader includes a vehicle proper having boom arms 12 and a bucket 14, in themselves in general of known construction. The boom arms 12 are mounted for vertical swinging movements about a transverse axis 16 on the vehicle and are so moved by suitable devices such as double-acting hydraulic actuators or jacks 18 powered by suitable hydraulic power means (not shown).

The bucket 14 is mounted for tilting movements about a transverse axis 20 in the extended or swinging ends of the boom arms 12 and is tilted by a doubleacting hydraulic actuator or jack 22 having its base end pivotally mounted at 24 on the boom arms and its pis ton pivotally secured as at 26 to the bucket.

The means for controlling the tilting of the bucket 14 and maintaining it in its desired position includes a control unit indicated in its entirety at 28, which includes valve means 30, in turn including a housing 32 and a spool 34.

The valve 30 is preferably a.4-way, open center, closed motor port valve, of known construction and need not be describedv in detail, although certain aspects of it will be referred to hereinbelow. The spool has sections 34a, 34b and 34c, and an outwardly extending stem 36 having a cam follower 38 thereon engageable with a cam 40 mounted on the boom arms 12 and movable with the boom arms about the axis 16, for actuating the valve. Thespool 34 is biased outwardly by a compression spring 42 reacting against the housing 32, for retaining the cam follower in operative engagement with the cam 40.

The actuator 22 is provided with hydraulic lines leading to the valve 30 from which additional lines 48, 50 continue, the line 48 proceeding; through a pump 52 and then into the reservoir 54, and the line 50 also communicating with the reservoir.

The valve housing 32 is provided with an upwardly extending arm 56 and a downwardly extending arm 58, the housing for convenience being assumed as having a starting position in which the arms are vertical as indicated by the line 60. The construction includes a feedback linkage 62 which preferably is in the form of a bowden wire having an outer tube or casing 64 and a wire 66 therein. One end of the tube 64 is fixedly secured at 68 to the extended end of one of the boom arms while the other end is fixedly secured at 70 to the frame of the vehicle. The wire 66 is secured at one end at 72 to a fixed element of the bucket 14, while the other end is secured to the arm 56 at 74.

Operatively secured to the downwardly extending arm 58 of the unit 28 is a manually operated device indicated as a unit at 76 which includes a yoke or fork 78 having jprongs 80, 82 slidable on a guide or bar 84 mounted at 86 on fixed elements of the vehicle frame. A connecting element 88 is pivotally mounted at 90 to the downwardly extending arm 58 and is slidable on the guide 84. Preferably a compression spring 92 is interposed between the connecting element 88 and the fork arm 82 for purposes to be referred to hereinabelow. The unit 28 then assumes'a floating support, and a floating condition being supported at both its upper and lower ends for swinging movement of each end about a pivot axis at the other end. in respective movements.

A manually actuated lever 94 is pivotally mounted at 96 on a fixed element 98 of the vehicle, and has a slotpin connection 100 with the fork 78. Suitable means may provided for frictionally retaining the lever 94 in manually adjusted position which may for convenience be an arcuate piece 102 having a knurled or roughened surface engageable by the lever.

In the operation of the device a starting position is assumed in which the bucket is in lowermost position and tilted forwardly as shown in FIG. 1 in full lines, and in FIG. 2. The position of the bucket shown may be utilized for filling it, and then to tilt the bucket to level position, the lever 94 is swung clockwise toward a position shown in FIG. 3. This movement throws the lower end of the valve housing 32 in the same direction (to the right), as represented in FIG. 3, whereby the spool is relatively moved in opposite direction (to the left) by the compression spring 42, this movement then shifting the section 34(- into communication with the hydraulic lines between the pump and the actuator 22. The fluid then flows from the line 48 leading from the pump, through the spool section 340 and then into the line 46, contracting the actuator 22 and thereby tilting the bucket toward level or upright position. this tilting movement of the bucket draws the wire 66 in corresponding direction, (to the left, FIG. 2) moving it relative to the tube 64 which is fixed to the frame, and correspondingly moving the arm 56 of the valve housing in the same direction, (to the left, FIG. 2). This movement of the valve housing produces relative inward movement of the spool (to the right since the spool is held against positive displacement in outward direction by the cam 40. This relative movement of the spool then brings the spool to the neutral position presented in FIG. 2 wherein the lines 44, 46 are shut off, and a circuit is completed through the pump by lines 48, 50.

According to the inherent characteristics of the valve 30, the controlling action is progressive i.e., not on-off, or step by step. In the operation just described, the spool 34 may not have been shifted a complete section displacement, but only partially in such direction to a position in which the flow of hydraulic fluid to the actuator 22 is only partial, and when the bucket 14 reaches its level position it gradually moves the spoolin the oppositedirection and gradually shuts off the flow of fluid to the actuator, and when the spool reaches a neutral position the flow ceases and the bucket remains in corresponding tilted position.

The arrangement provides for maintaining the bucket in the desired tilted position during vertical movements of the boom arms, and this is accomplished through the cam in conjunction with the feedback linkage. The cam is so shaped that as the boom arms rise the cam forces the spool 34 in inward direction (to the right, FIG. 2) against the spring 42 and moves the spool again toward its neutral position, and again reducing or shutting off the flow of fluid to the actuator 22. The extent of raising the boom arms is controlled by other control means (not shown) under the manual control of the operator. Regardless of the height to which the boom arms are raised under such control, the cam 40 actuates the valve spool an amount according to that height, through the characteristic shape of the cam. If the boom arms are raised to their maximum height, for example, the valve spool may be shifted to full neutral position, in a maximum positioning of the lever 94, but such a situation is not necessary for effective operation because if, in another example, the boom arms should be raised one-half their full height where the cam 40 would not be thrown to its full effective position, and brought to rest there, and the spool were not shifted to full neutral position, the bucket would continue to move in corresponding direction,

and acting through the feedback linkage 62 would move the valve housing in a continuing movement to relatively move the spool to its neutral position.

Thus the movement of the boom arms, acting through the cam 40 and the valve spool, controls the flow of hydraulic fluid to the actuator 22, but in any stationary position of the boom arms, whether fully lowered, fully raised, or at any position therebetween, movement of the bucket 14 effects continuing relative movement of the valve spool so as to bring it to its neutral position according to the desired position of the bucket regardless of the position of the boom arms.

The opposite movements of the various movable members are accomplished in a substantially opposite pattern of controls and movements. For example to tilt the bucket 14 forward, the lever 94 is tilted in counterclockwise direction, correspondingly shifting the lower end of the valve housing (to the left, FIG. 2) and the spool 34 is relatively moved to the right, placing the section 34a in operative position. This arrangement connects the hydraulic lines 48, 44 and extends the actuator 22, tilting the bucket in the direction referred to. As the bucket continues to tilt in that direction, it is operative through the feedback linkage 62 for swinging the upper end of the valve housing to the right, enabling the valve spool to again shift relatively to the left and to bring it back to neutral position.

As the boom arms move in lowering direction and considering a given position of the bucket on the boom arms, the shape of the cam 40 enables the spool to be moved relatively outwardly (to the left, FIG. 2) placing the section 340 of the spool in active position (FIG. 4) and contracting the actuator 22, tilting the bucket in corresponding direction (clockwise, FIg. 2). When the lowering movement of the boom arms ceases, whether in an intermediate position, or in lowermost position, the valve spool would be relatively extended, with the section 340 in active position, effecting continued movement of the bucket in the direction noted, but in that continued movement, the bucket acting through the feedback linkage 62, draws the upper end of the valve housing (to the left, FIG. 2) and moves the valve spool relatively to the right and to neutral position.

Referring again to the manually actuated lever 94, the compression spring 92 is interposed between the fork arm 82 and the element 88 to enable full and effective movement of the lever arm in corresponding direction (counterclockwise, FIG. 2) for tilting the bucket in lowering direction. Since movement of the manual lever in the direction noted, works toward moving the valve spool into engagement with the cam 40, the spring 92 provides a cushion enabling the fork 78 to be moved up fully to the position determined by the movement of the lever 94. If the cam 40 should be in a position limiting movement of the spool less than the movement of the lever 94, the spring 92 will yield and thereafter bias the valve housing, and thereby the spool, in the same direction as either the housing or the cam recedes. On the other hand when the valve housing is moved in the opposite direction, or away from the cam 40, such a spring is unnecessary, as between the fork arm and the element 88.

FIGS. 3, 4 and 5 are fragmentary views showing various positions of the movable elements utilized in the control and operating movements of the construction.

as described above, certain of the positions and elements therein being exaggerated for convenience in observing the relationship between the various elements.

In FIG. 3 the full lines show extreme position when the manual lever 94 is swung clockwise, swinging the lower end of the valve housing in corresponding direction,

and the dot-dash line shows the lower end swung in the opposite direction.

FIG. 4 shows in full lines the lower end of the valve housing in a fixed or neutral position and the upper end swung to the right in full lines, and to the left in dotdash lines.

FIG. 5 shows the valve housing in a straight vertical position with the valve positioned therein according to the raised position of the boom arms wherein the cam 40 has moved the valve spool inwardly or to the right. this being in contrast to FIG. 2 wherein the boom arms are in lowered position and the cam permits the valve spool to be moved to outwardly or the left.

I claim:

1. A loader bucket construction for use in conjunction with a vehicle having hydraulic power means, boom arms pivotally mounted for vertical swinging movements, a bucket mounted on the extended ends of the boom arms for tilting movements on a transverse axis, a hydraulic actuator on the boom arms for tilting the bucket, hydraulic lines interconnecting the power means and the actuator, said construction comprising a. valve means for controlling the hydraulic lines including l. a housing and a spool therein movable relative thereto,

2. the housing being mounted for movement at each of opposite ends,

3. means biasing the spool in an outward direction relative to the housing and means limiting its movement in that direction,

b. manually movable means for moving one end of the valve housing, which moves relative to the fixed position of the spool, for thereby adjusting the valve for controlling the flow of hydraulic fluid to the actuator and correspondingly tilting the bucket, and

c. means actuated by the bucket in the resulting tilting movement thereof for moving the other end of the housing in direction effectively opposite to the movement effected by the manual means, relative to the fixed position of the spool, this movement thereby adjusting the valve terminate the flow of hydraulic fluid to the actuator at a predetermined tilted. position of the bucket which corresponds with the position to which the manually movable means is moved.

2. A loader bucket construction according to claim 1 wherein the valve housing is movable in each of opposite directions at each end, and the valve is thereby capable of being set for effecting tilting movements of the bucket in corresponding opposite directions.

3. A loader bucket construction according to claim 1 wherein the means actuated by the bucket includes an element connected with said other end of the housing and with the bucket at a point eccentric to the tilting axis ofthe bucket, whereby upon tilting movements ofthe bucket said element is moved in corresponding directions for moving the valve housing as stated.

4. A loader bucket construction according to claim 3 wherein the means actuated by the bucket includes a bowden wire having an outer tube fixed at one end to a fixed portion of the vehicle and at its other end fixed to the boom arms, and said element of that means constitutes a wire within said tube and movable within the tube for effecting movement of the valve housing as stated.

5. A loader bucket construction according to claim 1 and including cam means actuated by the boom arms and operative for moving the valve spool relative to the valve housing responsive to vertical movements of the boom arms for correspondingly setting the valve means and thereby controlling the position of the bucket to maintain it in a tilted position relative to the ground in any vertical position of the boom arms.

6. A loader bucket construction according to claim 5 wherein the cam means on the boom arms forms the means (a), (3) for limiting the outward movement of the valve spool.

7. A loader bucket construction according to claim 6 wherein the valve housing is movable in each of opposite directions at each end, the valve spool is effectively moved inwardly or outwardly according to opposite vertical movements of the boom arms for correspondingly setting the valve means in respective vertical movements of the boom arms.

8. A loader bucket construction for use with a vehicle having hydraulic power means, boom arms pivotally mounted for vertical swinging movements, a bucket mounted on the extended ends of the boom arms for tilting movements on a transverse axis, a hydraulic acutator on the boom arms for tilting the bucket, hydraulic lines interconnecting the power means and the actuator, said construction comprising a. valve means for controlling the hydraulic lines including l. a housing mounted at opposite ends for reciprocating movement at each end about a pivot axis at the other end whereby the intermediate portion between the ends is free of mounting other than the mounting at the ends, whereby to enable.

the intermediate portion to float according to movements of the ends, 2. a spool in the housing movable relative thereto,

b. a hand lever mounted on the vehicle for moving a first end of the valve housing in each of its reciproeating directions throughout a. range of movement of the hand lever.

c. a bowden wire construction interconnecting the bucket and the second end of the valve housing including an outer tube secured at one end on a fixed portion of the vehicle and at its other end on the boom arms, and a central wire slidable longitudinally within the tube and having one end secured to the bucket at a point eccentric to its tilting axis and its other end secured to said second end of the valve housing, whereby upon vertical movements of the boom arms, the central wire moves said second end of the valve housing in respective directions,

d. movement of either end of the valve housing resulting in movement of the valve housing relative to the fixed position of the valve spool whereby to set-the valve for controlling flow of hydraulic fluid to the actuator, and

e. cam means operated by the boom arms, and operative in response to vertical movements of the boom arms for effecting movement of the valve spool relative to the valve housing whereby to vary the setting of the valve as previously made by the movements of the ends of the valve housing,

f. the relative movements between the valve housing and the valve spool in response to movement of the ends of the valve housing and the valve spool itself,

resulting in corresponding adjustments of the valve means for maintaining the bucket at a predetermined tilted position relative to the ground irrespective of the movements of the boom arms in either upward or downward direction.

9. A loader bucket construction according to claim 8 and including means for frictionally but releasably securing the hand lever at any set position within its range of movement.

10. A loader bucket construction according to claim 8 wherein the hand lever. in a first direction of movement thereof, moves the valve housing in such direction as to tend to move the spool toward the cam. and resilient means is interposed between the hand lever and the valve housing.

11. A loader bucket construction according to claim 10 wherein the lever operates to non-yieldingly move the valve housing in the opposite direction.

12. A loader bucket construction according to claim 8 and including means independent of the hand lever for supporting the corresponding end of the valve housing and for guiding it in transverse movements as moved by the hand lever.

boom arms pivotally mounted on a transverse axis for vertical swinging movements, a bucket mounted on a transverse axis on the extended ends of the boom arms for tilting movements relative to the boom arms. a hydraulic actuator on the boom arms for so tilting the bucket, means for transmitting power from the power means to the actuator, the construction comprising valve means for controlling the flow of hydraulic fluid to the actuator, the valve means including a housing and spool both of which are movable, means for normally retaining the housing and spool stationary. manual means for moving a first one of the housing/spool to a position wherein the hydraulic fluid flows to the actuator in a predetermined direction for correspondingly tilting the bucket, and control means responsive to the tilting movements of the bucket 'for moving the other one of the housing/spool to a position operative for limiting tilting movements of the bucket according to setting of the manual means. 

1. A loader bucket construction for use in conjunction with a vehicle having hydraulic power means, boom arms pivotally mounted for vertical swinging movements, a bucket mounted on the extended ends of the boom arms for tilting movements on a transverse axis, a hydraulic actuator on the boOm arms for tilting the bucket, hydraulic lines interconnecting the power means and the actuator, said construction comprising a. valve means for controlling the hydraulic lines including
 1. a housing and a spool therein movable relative thereto,
 2. the housing being mounted for movement at each of opposite ends,
 3. means biasing the spool in an outward direction relative to the housing and means limiting its movement in that direction, b. manually movable means for moving one end of the valve housing, which moves relative to the fixed position of the spool, for thereby adjusting the valve for controlling the flow of hydraulic fluid to the actuator and correspondingly tilting the bucket, and c. means actuated by the bucket in the resulting tilting movement thereof for moving the other end of the housing in direction effectively opposite to the movement effected by the manual means, relative to the fixed position of the spool, this movement thereby adjusting the valve terminate the flow of hydraulic fluid to the actuator at a predetermined tilted position of the bucket which corresponds with the position to which the manually movable means is moved.
 2. the housing being mounted for movement at each of opposite ends,
 2. A loader bucket construction according to claim 1 wherein the valve housing is movable in each of opposite directions at each end, and the valve is thereby capable of being set for effecting tilting movements of the bucket in corresponding opposite directions.
 2. a spool in the housing movable relative thereto, b. a hand lever mounted on the vehicle for moving a first end of the valve housing in each of its reciprocating directions throughout a range of movement of the hand lever, c. a bowden wire construction interconnecting the bucket and the second end of the valve housing including an outer tube secured at one end on a fixed portion of the vehicle and at its other end on the boom arms, and a central wire slidable longitudinally within the tube and having one end secured to the bucket at a point eccentric to its tilting axis and its other end secured to said second end of the valve housing, whereby upon vertical movements of the boom arms, the central wire moves said second end of the valve housing in respective directions, d. movement of either end of the valve housing resulting in movement of the valve housing relative to the fixed position of the valve spool whereby to set the valve for controlling flow of hydraulic fluid to the actuator, and e. cam means operated by the boom arms, and operative in response to vertical movements of the boom arms for effecting movement of the valve spool relative to the valve housing whereby to vary the setting of the valve as previously made by the movements of the ends of the valve housing, f. the relative movements between the valve housing and the valve spool in response to movement of the ends of the valve housing and the valve spool itself, resulting in corresponding adjustments of the valve means for maintaining the bucket at a predetermined tilted position relative to the ground irrespective of the movements of the boom arms in either upward or downward direction.
 3. A loader bucket construction according to claim 1 wherein the means actuated by the bucket includes an element connected with said other end of the housing and with the bucket at a point eccentric to the tilting axis of the bucket, whereby upon tilting movements of the bucket said element is moved in corresponding directions for moving the valve housing as stated.
 3. means biasing the spool in an outward direction relative to the housing and means limiting its movement in that direction, b. manually movable means for moving one end of the valve housing, which moves relative to the fixed position of the spool, for thereby adjusting the valve for controlling the flow of hydraulic fluid to the actuator and correspondingly tilting the bucket, and c. means actuated by the bucket in the resulting tilting movement thereof for moving the other end of the housing in direction effectively opposite to the movement effected by the manual means, relative to the fixed position of the spool, this movement thereby adjusting the valve terminate the flow of hydraulic fluid to the actuator at a predetermined tilted position of the bucket which corresponds with the position to which the manually movable means is moved.
 4. A loader bucket construction according to claim 3 wherein the means actuated by the bucket includes a bowden wire having an outer tube fixed at one end to a fixed portion of the vehicle and at its other end fixed to the boom arms, and said element of that means constitutes a wire within said tube and movable within the tube for effecting movement of the valve housing as stated.
 5. A loader bucket construction according to claim 1 and including cam means actuated by the boom arms and operative for moving the valve spool relative to the valve housing responsive to vertical movements of the boom arms for correspondingly setting the valve means and thereby controlling the position of the bucket to maintain it in a tilted position relative to the ground in any vertical position of the boom arms.
 6. A loader bucket construction according to claim 5 wherein the cam means on the boom arms forms the means (a), (3) for limiting the outward movement of the valve spool.
 7. A loader bucket construction according to claim 6 wherein the valve housing is movable in each of opposite directions at each end, the valve spool is effectively moved inwardly or outwardly according to opposite vertical movements of the boom arms for correspondingly setting the valve means in respective vertical movements of the boom arms.
 8. A loader bucket construction for use with a vehicle having hydraulic power means, boom arms pivotally mounted for vertical swinging movements, a bucket mounted on the extended ends of the boom arms for tilting movements on a transverse axis, a hydraulic acutator on the boom arms for tilting the bucket, hydraulic lines interconnecting the power means and the actuator, said construction comprising a. valve means for controlling the hydraulic lines including
 9. A loader bucket construction according to claim 8 and including means for frictionally but releasably securing the hand lever at any set position within its range of movement.
 10. A loader bucket construction according to claim 8 wherein the hand lever, in a first direction of movement thereof, moves the valve housing in such direction as to tend to move the spool toward the cam, and resilient means is interposed between the hand lever and the valve housing.
 11. A loader bucket construction according to claim 10 wherein the lever operates to non-yieldingly move the valve housing in the opposite direction.
 12. A loader bucket construction according to claim 8 and including means independent of the hand lever for supporting the corresponding end of the valve housing and for guiding it in transverse movements as moved by the hand lever.
 13. A loader bucket construction for use in conjunction with a vehicle having hydraulic power means, boom arms pivotally mounted on a transverse axis for vertical swinging movements, a bucket mounted on a transverse axis on the extended ends of the boom arms for tilting movements relative to the boom arms, a hydraulic actuator on the boom arms for so tilting the bucket, means for transmitting power from the power means to the actuator, the construction comprising valve means for controlling the flow of hydraulic fluid to the actuator, the valve means including a housing and spool both of which are movable, means for normally retaining the housing and spool stationary, manual means for moving a first one of the housing/spool to a position wherein the hydraulic fluid flows to the actuator in a predetermined direction for correspondingly tilting the bucket, and control means responsive to the tilting movements of the bucket for moving the other one of the housing/spool to a position operative for limiting tilting movements of the bucket according to setting of the manual means. 